1. Field of the Invention
The present invention relates to an organic electroluminescent panel and an organic electroluminescent display device. More specifically, the present invention relates to an organic electroluminescent panel having a structure in which an organic electroluminescent element is arranged above a thin film transistor, a wiring, and the like with an insulating film therebetween; and an organic electroluminescent display device including the organic electroluminescent panel.
2. Description of the Related Art
An organic electroluminescent (hereinafter, also referred to as an “organic EL”) display device is a display device which includes an organic EL panel, and the organic EL panel includes self-emitting elements, i.e., organic EL elements arrayed as a light source. This organic EL display device has an advantageous structure in principle, for example, in terms of reduction in thickness and weight, improvement in viewing angle and moving image characteristics, and decrease in electric power consumption and the number of components, although it still has room for improvement in extension of lifetime of the organic EL element and increase in size of the display, and the like. Therefore, the organic EL display device is a very promising next-generation thin display device, and therefore it has been actively researched and developed to be practically and widely used.
Further, high-definition images can be displayed in a display device including many pixels, such as a TV and a monitor, and therefore, in such a display, an active matrix system is commonly used for controlling driving of the pixels. According to the active matrix system, a thin film transistor (hereinafter, also referred to as a “TFT”) is formed in each of pixels arranged in a matrix pattern, and by switching this TFT using a control signal, a voltage applied to the respective pixels is controlled and thereby images are displayed. However, according to the active matrix system, the TFT and wirings connected thereto need to be arranged in each of the pixels, and therefore, a proportion of an area of the display region relative to an area of the entire pixel region, that is, an aperture ratio is reduced.
As a method for increasing the aperture ratio, a structure in which an interlayer insulating film for flattening is formed to cover the TFT and the wirings, and on this interlayer insulating film, organic EL elements are formed, is effective in an active matrix organic EL panel (for example, refer to Patent Document 1). The Patent Document 1 discloses a polyimide coating film, and a SiO2 film as the interlayer insulating film. An organic material is preferably used as a material for the interlayer insulating film, commonly. This is because the use of the organic material is advantageous for the interlayer insulating film to secure a thickness larger than a specific thickness, in terms of simplification of production processes, reduction in production costs, and the like. However, the organic material easily absorbs moisture. Therefore, such an interlayer insulating film composed of an organic material has been known to have influences such as a reduction in luminance of light emitted from the organic EL element.
For this problem, a method of preventing the influences on the organic EL element by a configuration in which the organic insulating film is covered with an inorganic insulating film is disclosed (for example, refer to Patent Documents 2 to 4). A method in which the substrate is heated or placed under a vacuum atmosphere to be subjected to a dehydration treatment, thereby preventing influences of residual moisture on the organic EL element is disclosed (for example, refer to Patent Document 5). However, even if these methods are used, pixel shrinkage (refer to FIG. 4), i.e., a problem in which a luminance of emitted light is reduced with time, starting from the peripheral part of the display region of the organic EL panel, can not be completely prevented. Therefore, such methods still have room for improvement.    Patent Document 1: Japanese Kokai Publication No. Hei-10-189252    Patent Document 2: Japanese Kokai Publication No. 2001-356711    Patent Document 3: Japanese Kokai Publication No. 2005-26103    Patent Document 4: Japanese Kokai Publication No. 2004-241247    Patent Document 5: Japanese Kokai Publication No. 2001-196188